One known prior art related to such storage cases for packaging recording medium discs such as CDs, DVDs and LDs is described in Japanese Examined Patent Publication No. HEI 6-51506 (corresponding to U.S. Pat. No. 4,874,085).
This prior art storage case is constructed to support a disc only at its central area free of information carrying tracks and not to contact the area containing information carrying tracks of the disc by providing a predetermined clearance therebetween, so as not to transfer any deformation of the case to the disc.
Thus, this construction requires that the case have a higher rigidity so as to minimize its possible deformation, and make such clearance relatively large. This results in a drawback that the case has a relatively large thickness.
The storage case having an increased thickness involves problems such as a larger storage space needed for such cases and more frequent replenishment of goods on display due to a decreased number of discs which are displayable at a time, for example, in displaying and selling.
Accordingly, a storage case of this type has been desired to have a decreased thickness.
To this end, the art of reducing such clearance by supporting a disc at its outer peripheral edge area as well as at its central area, has been developed as disclosed, for example, in Japanese Unexamined Patent Publication No. SHO 60-148485.
Though this art employs a structure for supporting the disc at both the central and outer peripheral areas thereof, other structures, particularly for holding the central hole portion of the disc, remain conventional and, hence, it is impossible to decrease the thickness of the storage case as desired.
Typically known such structure for holding the central hole portion of a disc is described, for example, in Japanese Examined Utility Model Publication No. HEI 3-31748.
This conventional structure includes a boss portion to be fitted into the central hole of the disc, the boss portion defining a multiplicity of radially extending slits which are circumferentially equally spaced from each adjacent one. These slits form elastic pieces adapted to support the central area of the disc elastically.
With this structure the projecting amount of the boss portion to project from the upper side of the disc held by the boss portion is required to be relatively large so as to prevent an unexpected removal of the disc from the boss portion. For this reason it has been difficult to make the storage case thinner.
Also, this central hole portion holding structure has been desired to allow the disc to be removed by a simple operation as well as to hold the disc securely.
Although this conventional structure is capable of securely holding the disc by means of the multiplicity of elastic pieces for elastically supporting the disc, the removal of the disc therefrom is not easy because an increased pressing force is required to depress the elastic pieces for the removal.
Further, since constantly biasing the periphery of the central hole of the disc with an increased pressing force for secure holding is likely to cause the disc to warp, the holding structure has been desired to support the disc with a smallest possible force.
This means that the structure for holding the central hole portion of the disc has been desired to satisfy incompatible requirements: holding the disc with a smaller force, holding the disc securely, and allowing the disc to be removed by a simple one-touch operation.
In view of these requirements a storage case has been devised having a reduced number of elastic pieces located at three circumferential points and enabling a one-touch removal of a disc, as disclosed, for example, in German Patent DE3425579.
In this conventional storage case, however, the inner ends of the three elastic pieces are connected to a disc-like push member and, hence, a force working on this push member also works on the three elastic pieces at the same time. Accordingly, an increased force is required to deform these elastic pieces.
In addition, this storage case requires a compressed elastic element, a nip protuberance and the like for ensuring a one-touch removal of the disc, which makes the construction more intricate, thus resulting in a difficulty in making the storage case thinner.